In U.S. patent application Ser. No. 10/690,100 filed Oct. 21, 2003 and entitled “METHOD AND APPARATUS FOR FORMING A THREADED HOLE IN A HYDROFORMED PART” and assigned to the assignee of this invention, there is disclosed a tool for piercing a hole in a hydroformed part and then forming a thread in the hole while the part remains in the hydroforming dies following its hydroforming. Wherein the tool which is referred to as a hydrotapping tool (1) first pierces the hole in a tool advancing tool operation while the hydroforming pressure is maintained, (2) then extrudes the wall about the hole in a continued tool advancing operation to thereby deepen the hole, (3) then sizes the deepened hole in a continued tool advancing operation, (4) then in a turning and advancing tool operation forms a thread in the hole in a metal displacing operation, and (5) then is retracted from the threaded hole while being rotated in the opposite direction in order to release the tool from the threaded hole. And wherein in the thread forming operation, the tool must be fed at a feed rate equal to that of the thread forming portion of the tool and at this same feed rate but in the opposite direction in order to retract the tool from the threaded hole without wiping out the formed thread.
While a power arrangement suitably adapted to powering the tool as disclosed in the aforementioned U.S. patent application Ser. No. 10/690,100 would be satisfactory in many cases, there remains a need for a rugged and highly reliable power unit for powering such a tool in meeting the demands of high volume production. Such as for example the hydroformed parts used in mass-produced motor vehicles. Wherein one or more threaded holes are required in the hydroformed part and each threaded hole must be accurately located and the thread formed therein made strong and precise and all without producing slugs and metal cuttings that could enter the part and contaminate the hydroforming apparatus. Such as is the case with use of the above tool that pierces, extrudes and forms a thread in the thus produced deepened hole and as distinguished from the use of a drill, extruding pin and thread cutting tap to form the required threaded hole.